Methods of boning, grinding, and subsequent packaging of beef in a substantially oxygen-free environment have been disclosed in PCT/US01/45146. In one aspect, these steps occurred in an essentially continuous and enclosed conduit. The method results in a food item, such as beef, having high amounts of deoxymyoglobin. The beef, high in deoxymyoglobin, is then packaged in oxygen free individual trays and depending on the ultimate destination, may be packaged in master containers. Master containers are used to transport the individual beef packages in a substantially oxygen-free state up to the point of sale. In either event, however, it is desirable that oxygen is exchanged with the controlled atmosphere within the individual packages prior to sale to allow the beef to produce a bright red color, known as “bloom” (or oxymyoglobin), that is visually pleasing to consumers. The previous application disclosed trays with means, such as apertures in the tray and in the overwrapping lidding webs at strategic locations to provide for the rapid exchange of the controlled gas within the packaged trays for the oxygen in air outside of the packaged trays while restricting leaking of liquid therefrom. Other ways of exchanging the controlled atmosphere for air and oxygen included an oxygen permeable package that comprises a polypropylene thermoformed tray with a plasticized polyvinyl chloride web hermetically sealed to the flanges of the tray. In this manner, gas exchange occurs by permeation through the permeable packaging materials.
When a retail package with controlled atmosphere therein is removed from an oxygen-free atmosphere and placed in the normal ambient air atmosphere, the controlled gas in the free spaces on the inside of the package is displaced by atmospheric gases over time by the normal process of diffusion. It has been observed that a deleterious phenomena can occur to the beef if the oxygen content in the packages is not elevated from 0.05% to at least 3% oxygen within about 15 minutes, and sometimes this effect even occurs if the oxygen content of the package is not elevated from 0.05% to at least 10% oxygen within about 10 minutes. Without this rapid elevation in oxygen content, it has been observed that the physical and chemical mechanisms taking place on the surface of the beef favor the production of increased amounts of undesirable metmyoglobin relative to the desirable brightly colored red oxymyoglobin. Therefore, it is advantageous to produce methods and materials to exchange gases within the allotted time to reduce the production of metmyoglobin and the unsightly appearance caused by it.
Microperforated wrapping materials have been known and used in the food industry; however, one drawback that has been observed is “weeping” or the purge of liquids associated with the meat contents through the microperforations. This weeping effects the quality of the packaged meat in two ways. First, condensation from the weeping liquids can accumulate on the internal surfaces of the retail package. These water droplets can hinder the diffusion of gases to the extent that the gas exchange can be slowed to several hours. Second, previous attempts to use microperforated materials as an overwrapping web material resulted in direct contact of the microperforated web with the food item of the package. It was later found that weeping of liquids through the package as a result of this contact, occurred to such an extent that made it unacceptable to consumers.
Therefore, there is a need to refine the methods and materials useful in the packaging of perishable food items within enclosed conduits, including the use of microperforated lidding webs to provide a desired gas diffusion rate without allowing the escape of liquids from the package. Also lacking in the prior art are methods and apparatus that can apply longitudinal and lateral tension on a web of lidding material. The present invention fulfills these needs and provides further related advantages.